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The Cold spray method of material deposition is widely used for surface enhancement, to improve properties such as corrosion and wear. A detailed microstructural analysis of cold sprayed Ni based coatings (IN625 (Inconel 625 is a Trademark of Huntington alloys corporation) using the transmission electron microscope, revealed the occurrence of three distinct types of microstructures in the as sprayed condition, adjacent to each other. These include the occurrence of large (> 1 μm) grains having a high dislocation density, along with regions comprising shear bands (20-30 nm wide) and twins with a large aspect ratio (> 1000), along with locations having a very fine grained structure (20-30 nm). The crystallite size, using a Hall-Williamson plot measures an average 50 nm. The substrate deformation indicates a bilayer dynamic recrystallization, as a means to accommodate the strain. The microscopy studies will serve to correlate the bonding mechanism of cold sprayed IN625 on 4130 steel.

The Ni-Mn-Ga Ferromagnetic shape memory alloys are becoming an important element of sensor and actuator materials due to their large magnetic-field-induced strain and shape memory effect in recent years. The martensitic transformation temperature of the Heusler alloy system has been intensively studied. The Ni 54.8 Mn 23.2 Ga 21.7 irregular agglomerated nanoparticles were prepared by ball milling method, and characterized by x-ray diffraction, differential scanning calorimetry and transmission electron microscopy techniques. These particles reveal a disordered non modulated face centered tetragonal structure. For the first time, nanopowder has been found to undergo a sequence of temperature-induced intermartensitic transformation in addition to the martensitic transformation on cooling. It is believed that relaxation of internal stresses is the main issue in this case. The resistivity of the material has been measured on cooling from 450 K to 300 K. It is observed that the resistivity is maximum in the nano crystalline state and it decreases substantially with decrease of the temperature. Both amorphous and nanocrystalline material coexisted in the ball-milled sample, such a nanomagnetic structure is considered to be ideal for soft nanomagnetic material.

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